1. Field of the Invention
This invention relates generally to seals used in the container manufacturing industry when such containers are being tested for leaks, and more specifically relates to a seal having performance characteristics that allow it to be used as a seal for cans of widely varying characteristics.
2. Description of the Prior Art
Prior to the invention of the seal member disclosed hereinafter, manufacturers of aluminum and steel cans have been required to maintain in their inventory a multitude of seals of differing characteristics so that containers of differing characteristics could be tested. In other words, certain types of containers may require the use of very soft seals when such cans are leak tested, whereas other types of cans may require the use of very hard seals during such tests. Of course, the testing of most cans requires the use of seals harder than the softest seal and softer than the hardest seal. Accordingly, a complete line of seals of differing degrees of hardness have been developed by the industry, and the seal having the characteristics closest to the optimal characteristics for a particular application is selected from among all the seals available when tests are to be performed on a certain type of container.
The current state of affairs is clearly undesireable due to the low productivity associated with the task of attempting to match the appropriate seal to the container types to be tested. Mismatches commonly occur, with the result that adequately constructed cans may be rejected or, even more catastrophic, defective cans may pass the tests.
Soft seals are generally desireable, because their resiliency allows them to accommodate cans of varying lengths. (A batch of manufactured cans may vary in length by about 40/1000ths of an inch). Further, such softness permits the sealing of cans having acceptable deformities such as flanges that are only slightly out of round, or flanges having burrs which are allowed by tolerance specifications.
The primary objectional quality of soft seals, however, is their propensity to deteriorate quickly, i.e., soft seals have short useful lifetimes. The soft seals are subject to abrasion by sharp flanges and may be damaged by unflanged cans as well. Seal abrasion is disasterous since such abrasion will prevent the seal from performing its intended function-sealing a container while the container is leak tested-with the result that good cans will be rejected as leaky even though the source of the leak is the abraded seal. Often, a seal abrasion is not detected until an unusually high number of cans have been rejected, thereby casting doubt upon the effectiveness of the seal.
Abrasions also cause the cans to fail to separate from the seal after the leak test has been completed, and this failure to separate causes discharge jams which of course cause downtime.
Another serious drawback of soft seals is their ability to seal cans having microsplits in their flanges. This allows defective cans to pass the leakage test. When a bottler discovers such a leak in a can that has passed a test that supposedly ensures 100% detection of leaky cans, all cans in the suspect lot are destroyed. Thus, each mistake is multiplied many times over.
Hard seals, therefore, are often used because such seals do not seal microsplits and are also abrasion-resistant. Unfortunately, hard seals are less able to provide effective seals for cans of differing lengths, or for cans having out of round or burr-carrying flanges. Moreover, the strain on the mechanical parts that drive the seals into sealing engagement with the cans to be tested after sealing is increased when hard seals are used since increased axially directed pressure must be imparted to such hard seals to insure adequate sealing.
There is clearly a need for a single seal member that combines the desireable features of hard and soft seals while overcoming the undesireable features of such seals, but the prior art contains no teachings or suggestions on how best to provide such a seal.